Gas from many wells does not meet the generally accepted pipeline specification of less than 1/4 grain hydrogen sulfide per 100 scf and 1 grain total sulfur per 100 scf. The most widely used method for removing acid gases from gas mixtures is to contact the gaseous mixture with an aqueous solution of an alkanolamine. The salts formed by alkanolamine and acid gases present (H.sub.2 S, CO.sub.2) can be decomposed by heating and/or stripping with steam. The alkanolamine solution is regenerated by heating or stripping which allows it to be recycled and reused.
This type of gas process is chemical in nature because chemical reactions are used to remove the acid gases. Another method is based on physical absorption, i.e. the extent to which the acid gases dissolve in the solution. Physical processing is most advantageous when the partial pressure of the acid gases is high, e.g. over 50 psig.
Prior art in gas processing using physical solvents includes: U.S. Pat. Nos. 2,518,752 Chapin, Aug. 15, 1950, 2,547,278 McCartney, May 3, 1957--a mixture of amines and glycols; U.S. Pat. Nos. 3,324,627 Kohrt June 13, 1956, 3,120,933 Thorman et al, Feb. 11, 1964--N-methyl-2-pyrrolidone (m Pyrol); U.S. Pat. No. 4,107,170 Ferrin et al, Aug. 15, 1978--1-formylpiperidine (sweet and dry); U.S. Pat. No. 3,594,985 Ameen et al, July 27, 1971--a mixture of polyethylene glycol dimethylethers (SELEXOL).
The prior art in gas processing using mixtures of an amine, physical solvent and water includes the following solvents: U.S. Pat. Nos. 3,347,621 Papadoulos et al, Oct. 10, 1967, 3,463,603 Freitas et al, Aug. 26, 1969--sulfolane (SULFINOL); U.S. Pat. No. 4,360,363 Ferrin et al, No. 23, 1982--4-propanolpyridine; U.S. Pat. No. 4,372,925 Cornelisse, Mar. 25, 1981--tetraethylene glycol dimethylether.
In the never-ending search for a better solvent, the present invention contemplates the use of N-2 methoxyethyl-2-pyrrolidone as a solvent. Proportioning N-2 methoxyethyl-2-pyrrolidone with amine and water optimizes the solution for selective removal of acid gases and mercaptans from gaseous mixtures.